In the previous patent application DE 103 26 181 it is described to substitute a part of the wood chips or fibres in the production of wood material boards, i.e. wood chip and wood fibre board in particular, by milled or defibrated agglomerate from mixed plastics from the refuse collection. The dimensions of the plastics particles on the one hand, and the wood chips or fibres on the other hand, are approximately equal. Thus, a possibility of a complete material utilization of mixed plastics has been created.
In current collection systems for refuse plastics, e.g. packaging material from consumer households, joghurt cups, protective wrappings, shopping bags, bottles for cleaning materials, toothpaste tubes and so on, mixed plastics are mostly obtained. Besides to the usual sheets and plastics from LDPE, HDPE or PP, they often comprise sheet remainders from polyamides, polycarbonates, PET or other plastics. The quantitative distribution of the content of the different plastics which are handed over to the processing and assorting plants by the collecting firms depends from the collecting behaviour and the quality-consciousness of the population. In spite of advanced assortment, a complete separation of the different kinds of plastics cannot be obtained. A clearly-sorted separation between LDPE sheets and HDPE sheets can be obtained with a quota of approximately 95%. However, besides there are collecting systems for LDPE and HDPE only, in which predominantly plastic sheets are collected which were produced via a sheeting calender.
Sheet or bottle fractions from collecting systems are crushed into flakes or chips, optionally after being cleaned and presorted. In order to get sufficient bulk density for transportation, the flakes or chips are processed into a granular material in a so-called agglomerating process. Depending on purity and sorting, the granular material is very uniform (at high degree of purity of the sorts of the plastics), or it has a very inhomogeneous structure from the viewpoints of appearance as well as from those of the consistency and geometry of the agglomerate (high degree of mixing of the most different sorts of plastics from various sources, e.g. mixed plastics from household collection systems). In the processing, the mentioned agglomerating, the flakes or chips are heated by friction in a stirring machine such that they melt on. By spraying of the warmed agglomerate with cold water, which is performed at intervals, a part of the organic constituents escapes via the water vapour. At the same time, the molten-on sheet pieces cool down and agglomerate into granulate-like, throwable bodies. The agglomerate has a relatively high bulk density and is very suited for transportation. Agglomerating methods have been described in AT 343445 or DE 198 01 286 C1, for instance.
In the substitution of wood chips or fibres through plastics, it is to be demanded that the plastics particles be similar to the substituted wood particles of chip board or fibre board in their geometric form and dimension, in order to obtain results that are similar to those of conventional wood material boards. As a consequence, in fibre materials the fibre content should prevail, and in chip materials the chip content.
The commonly produced agglomerate is present in very different forms and sizes, and thus it is not suited as a raw material in the production of wood materials, because strong demixing behaviour is presented in the blending process, due to the different sizes of the fractions. Board materials which are produced with these two fractions have an uneven surface appearance, mostly on the surface of the workpiece, which is due to local agglomerate accumulations, and thus they make the insufficient mixing of the two fractions visible. Further, the formation of a continuous plastics-plastics or plastics-wood texture, respectively, having a homogeneous texture structure, is not ensured due to the insufficient mixing. Furthermore, the desired mechanical properties, like transverse pull strength, flexural strength and also the desired behaviour in humid conditions, like swelling behaviour and water absorption, are not attainable.
As has been already described in the previous patent application, crushed agglomerate is used for these reasons, for which purpose different milling technologies can be used. For a producer of wood materials who wants to use milled plastics agglomerate, there only remains to buy milled plastics agglomerate from a third side or to invest into a sumptuous milling machine.
A similar problem results for producers which make materials from other fibrous materials, e.g. from vegetable fibres like those from flax or hemp, or even from glass or carbon fibres. When these fibres are to be mixed with fibres from recycled plastics in order to prepare a corresponding fibrous material, the plastics agglomerate should be milled by the producer himself, which requires a suitable milling machine, or it should be acquired in a milled form from a third side, which also requires a relatively high expenditure.
From U.S. Pat. No. 5,154,361A a method for crushing plastics parts has become known, in which a suspension of the plastics particles in water is passed through a disc refiner, together with an antifoaming agent. In one example, the suspension contains 3% solid matter. Cellulose fibres can also be admixed to the suspension.
From EP 0 588 023A a method for producing a compound body has become known, in which plastic-coated compound materials, preferably paper or cardboard, are used as the starting materials. The compound materials are crushed into particles and thereafter the mass is warmed to at least the melting temperature of the plastics of the compound materials and is bonded to each other under pressure. From DE 101 28 549 it has become known to produce performed parts from natural fibers or chips by adding a plastics polymer as a binder. The performed part is prepared without extrusion.